Using Kiln Dust to Improve Weak Subgrades for Pavement Construction: A Field Verification in Michigan, USA

Remove-and-replace with suitable material has been the primary solution used for improving subgrades in Michigan, USA, when weak subgrades are encountered in road construction. Considering the large extent of silty and clayey soils found in southeastern Michigan, where much of the population and the roads are located within the state, the earthwork associated with this solution is massive and expensive. The use of cement kiln dust (CKD) or lime kiln dust (LKD) as a subgrade stabilizer can be a cost-effective solution if there is sufficient evidence to prove that such stabilization is suitable for the soils and the climate in southeastern Michigan. This became the subject of a field and laboratory investigation carried out in Michigan and sponsored by the Michigan Department of Transportation. The findings from the laboratory portion of this research (which were published in a separate manuscript) proved CKD’s suitability for long-term stabilization and LKD’s capacity for being a stabilizer for short-term modifications of clayey soils found in southeastern Michigan. This study covers the field testing portion of this investigation. Two CKD-stabilized and another two LKD-stabilized subgrades, which were already in use for 4–6 years, were tested for strength, using dynamic cone penetration (DCP) tests. The California bearing ratios estimated from the DCP tests showed that the CKD-stabilized and LKD-stabilized subgrades could offer strength gains as high as 200–515% and 149–257% compared to in situ soils, respectively, even after 4–6 years in use.